1. Scientific Method – Experimental Design Controls and Variables

2. Scientific Experiments Follow Rules.
An experimenter changes one factor and observes or measures what happens.

3. Observation vs. Inference
Observation: Using one or more of the 5 senses to gather information
Inference: Development of ideas based on observations
Prediction: Use of knowledge to identify and explain observation or changes
Warm Up: Take 5 minutes to look at the jar on your table.
Write down ….. 4 observations
2 inferences

4. The Control Variable
The experimenter makes a special effort to keep other factors constant so that they will not effect the outcome.
Controls are NOT being tested
Controls are used for COMPARISON

5. Other Variables
The dependent variable is what the investigator measures (or counts or records).
For example, you may want
to study peanut growth. One
possible dependent variable
is the height of the peanut plants.

6. Other Variables
The independent variable is what the investigator deliberately varies during the experiment.

7. Example of Controls & Variables
An example, suppose you want to figure out the fastest route to walk home from school.
You will try several different routes and time how long it takes you to get home by each one.
Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

8. What are the Variables in Your Experiment?
Varying the route is the independent variable
The time it takes is the dependent variable
Keeping the same walker throughout makes the walker a control variable.

9. One more thing… it is best to make several trials with each independent variable.

10. Data = Information gained from observations
Quantitative Data: numerical data (measurements of time, temperature, length, mass, area, etc.)
Grass experiment = Area of healthy grass vs. area of dead grass
Qualitative Data: descriptions of what our senses detect
Grass experiment = More healthy grass vs. less dead grass